title: Improved cone-beam computed tomography in supine and prone breast radiotherapy. Surface reconstruction, radiation exposure, and clinical workflow.
abstract: OBJECTIVE
  Cone-beam computerized tomography (CBCT) enables three-dimensional information of the scanned region and provides soft tissue images with good spatial resolution. Our aim was to optimize image acquisition settings for prone and supine breast radiotherapy with respect to contour accuracy, clinical practicalities, and radiation dose.
  
  
  METHODS
  CBCT images were acquired for both prone and supine anthropomorphic phantoms and a female cadaver in supine and prone set-up. CBCT protocols were investigated by altering the tube current, exposure time, range of projection views, field of view (FOV), and starting angle. For clinical practicalities, the frequency of the use of an offset CBCT isocenter was evaluated at 558 205°-CBCTs (37 patients; 13 prone and 24 supine) and 1272 360°-CBCTs (102 patients; 13 prone and 89 supine).
  
  
  RESULTS
  Prone and supine breast CBCT images acquired with a bowtie filter, a small FOV, a range of projection views equaling 180°, a tube current of 20 mA and an exposure time of 32 ms, demonstrated adequate contour accuracy and an elimination of the offset CBCT isocenter procedure, while this occurred in 40.7 % for the old full-rotation protocol. Furthermore a 4.3-fold dose reduction was observed for the Computed Tomography Dose Index (CTDIw) compared to the preset Chest M20 protocol.
  
  
  CONCLUSIONS
  The established 180° protocol demonstrated acceptable contour accuracy, eliminated the CBCT isocenter offset procedure and reduced patient radiation exposure.
authors.affiliation: Department of Radiotherapy, Ghent University Hospital, De Pintelaan 185, 9000, Ghent, Belgium.
authors.forename: A
authors.initials: A
authors.lastname: De Puysseleyr
authors.forename: T
authors.initials: T
authors.lastname: Mulliez
authors.forename: A
authors.initials: A
authors.lastname: Gulyban
authors.forename: E
authors.initials: E
authors.lastname: Bogaert
authors.forename: T
authors.initials: T
authors.lastname: Vercauteren
authors.forename: T
authors.initials: T
authors.lastname: Van Hoof
authors.forename: J
authors.initials: J
authors.lastname: Van de Velde
authors.forename: R
authors.initials: R
authors.lastname: Van Den Broecke
authors.forename: C
authors.initials: C
authors.lastname: De Wagter
authors.forename: W
authors.initials: W
authors.lastname: De Neve
mesh_terms: D001943:Breast Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D002102:Cadaver; D054893:Cone-Beam Computed Tomography / Q000295:instrumentation / Q000379:methods*; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D056888:Patient Positioning / Q000379:methods*; D019047:Phantoms, Imaging; D016684:Prone Position; D011829:Radiation Dosage; D011835:Radiation Protection / Q000379:methods; D011856:Radiographic Image Enhancement / Q000379:methods*; D061089:Radiotherapy, Image-Guided / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D016683:Supine Position; D016896:Treatment Outcome; D057188:Workflow